Dredge Liver Slices In Flour, Shaking Off Excess, And Season With Salt And Pepper. Melt Butter In A Large Skillet Over Medium High Heat. Cook Liver For 5 Minutes Per Side, Reducing Heat If Necessary. Transfer To A Heated Serving Dish, And Keep Warm. In The Same Skillet, Increase Heat To Medium High And Add Tarragon Vinegar, Scraping The Bottom Of The Skillet With A Wooden Spoon. If Necessary, Add A Small Amount Of Water To Increase Sauce. Lay Lemon Slices Over Liver, And Pour Sauce Over The Top. Sprinkle With Freshly Chopped Parsley. Serve Immediately.